| Summary: | El Niño-Southern Oscillation (ENSO) is a climate phenomenon that causes large scaleclimate variability. It is a coupled mode of ocean-atmosphere interaction between sealevel pressure and sea surface temperature fluctuations in the equatorial Pacific. Typically, in order to observe the phenomena, an ENSO index is used, which is formed with sea surface temperature anomalies. Positive (El Niño phase) and negative (La Niña phase) temperature anomaly have different effects on a global scale. SST-based indexes are created by taking the average of four different regions. These regions, fromthe Peruvian shores to the center of equatorial Pacific, are listed as follows: NINO1+2, NINO3, NINO3.4 and NINO4. Indexes can create different oscillations during thesame period. In addition, even they differ in some regions the effect of each index issimilar. According to some studies (e.g. Ziv et al., 2006; Lolis & Türkeş, 2016) negative phase Arctic Oscillation affects temperature, sea level pressure and 500 hPa geopotential height anomalies (z500) of the Euro-Mediterranean region. Sen et al. (2019) mentioned that, in negative phases of AO and ENSO, strengthening East Asian trough pushes the Mediterranean trough towards west. Consequently, a dipole pattern forms over Euro-Mediterranean region. Sen et al. (2019) study suggested that, NINO1+2 index is more effective on dipole pattern, although NINO3.4 is commonly used. In this study, we investigated which ENSO index is more related to the dipole pattern in the Euro-Mediterranean region. Analyses were conducted for boreal winters (December-January-February) of 70 years between 1950-2019. Correlation analysis indicated that NINO1+2 index is better correlated with z500, sea level pressure and surface temperature than the other indices over the Euro- Mediterranean region. In addition, in the La Niña phase, it has a significant relationship with the omega blocking system formed over Europe. According to some studies (Pozo-Vazquez et al., 2001, 2005), the negative (cold) phase of ...
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